1. Field of the Invention
The present invention relates generally to integrated circuits. More specifically, but without limitation thereto, the present invention relates shielding integrated circuits from ionizing radiation and x-rays.
2. Discussion of the Background Art
In many radiation environments electronic circuits must be shielded from ionizing radiation and x-rays in order to function properly. For example, in a space environment, circuit die must be shielded from ionizing radiation or the circuit may fail to function properly. In other environments, e.g., where the risk of exposure to artificial nuclear radiation is high, the circuit must be shielded from x-rays.
Previous practices use an ionizing radiation shield to shield from ionizing radiation found in the natural space environment. Ionizing radiation found in the natural space environment is comprised primarily of electrons and protons with a small number of ionized highly energetic heavy ions. The electrons and protons contribute to the integrated radiation damage of a semiconductor device and is frequently called ionizing radiation. Ionizing radiation creates total dose damage in electronic circuits. The damage is frequently cumulative over the entire time the device is in space or in the ionizing radiation environment. Since, for the most part, the ionizing radiation found in space is isotropic, incomplete coverage of package shielding allows for only a percentage of radiation to leak through, which percentage can be predetermined. As shown in FIG. 1, by way of example, this radiation leakage occurs through the sides of the packaging where there is no radiation shielding material. Ionizing radiation comes from every direction, therefore allowing a certain amount of side radiation leakage is acceptable as long as it does not exceed the total dose tolerance of the circuit die.
In contrast, x-ray radiation resulting from, e.g., artificial nuclear detonations comes from substantially a single direction, which in many instances can not be predetermined. This type of x-ray radiation, or burst radiation, usually comes from a man-made event such as a nuclear detonation. X-ray radiation usually generates dose rate damage in electronic devices, because of the extremely short time frame that the burst exist. This type of damage is different from the slower total dose damage that occurs for the natural space radiation environment. X-ray radiation is electromagnetic and therefore the shielding effectiveness of materials is different from that of ionizing radiation. Additionally, since the direction from which x-ray radiation, such as burst radiation, will come can't be predetermined and because substantially all of such radiation comes from substantially a single direction, the shielding shown in FIG. 1 is insufficient as a very large dose of x-ray radiation could come from an angle which is not protected.
FIG. 1 illustrates a shielding package designed to shield from ionizing radiation, such as found in a natural space environment.
FIG. 1 shows a radiation shielding top 102, a radiation shielding bottom 104, a plurality of circuit die 106, a plurality of conductors 108, a base 110, and a line of sight angle 112.
As shown in FIG. 1, the plurality of circuit die 106 are shielded by the radiation shielding top 102 and the radiation shielding bottom 104. This shielding is sufficient to shield the plurality of circuit die 106 from an amount of radiation greater than the total dose tolerance of the plurality of circuit die 106. However, the line of sight angle 112 represents an exposed line of sight not protected by shielding material. Therefore, burst radiation coming from within the line of sight angle 112 may directly impact with the plurality of circuit die 106 and cause severe damage or destroy the operation of the plurality of circuit die 106.
Thus there is a need for package design to eliminate the problems discussed above.